Question

Calculate the number of atoms in each of the following:

1. 52 moles of Ar
2. 52 u of He
3. 52 g of He.

Answer 1

(i) 1 mole of Ar = 6.022 × 10²³ atoms of Ar
∴ 52 mol of Ar = 52 × 6.022 × 10²³ atoms of Ar
= 3.131 × 10²⁵ atoms of Ar

---

(ii) 1 atom of He = 4 u of He
Or,
4 u of He = 1 atom of He
1 u of He = \(\frac 14\) atom of He
52 u of He = \(\frac {52}{4}\) atom of He
= 13 atoms of He

---

(iii) 4 g of He = 6.022 × 10²³ atoms of He
∴ 52 g of He = 6.022 × 10²³ × \(\frac {52}{4}\) atoms of He
= 7.8286 × 10²⁴ atoms of He